1. Field of the Invention
The present invention relates to an electronic control unit containing therein a microprocessor for use in, e.g., fuel supply control of an automobile engine and, more particularly, to an on-vehicle electronic control unit improved in reliability of a control constant to be transmitted from a non-volatile program memory that is provided in a first control circuit section acting as a master station to a data memory that is provided in a second control circuit section acting as a substation in an electronic control unit including a plurality of control circuit sections electrically divided so as to exchange serial signals with each other.
2. Description of the Related Art
An electronic control unit arranged to exchange information by the method of serial communication between a plurality of control circuit sections sharing functions therebetween, as well as to detect communication error and perform error processing has been popularly put in practical use.
For example, the “On-Vehicle Electronic Control Unit” of the Japanese Patent Publication (unexamined) No. 333901/2002, discloses an on-vehicle electronic control unit provided with serial communication means that is formed of an integrated circuit section mutually communicating with a microprocessor and that is capable of transferring control constants at the start of operation or of mutually exchanging various data during the operation freely. In this prior art, specific constitution examples of a variety of communication packets are described in detail including retransmission processing in case of sum-check error or timeout check error with respect to a serial communication data.
Further, the “On-Vehicle Electronic Control Unit” of the Japanese Patent No. 3346163 discloses a technique, in which a ROM data, which is provided in the first microcomputer with regard to a control content of the second microcomputer, is repeatedly transmitted at intervals of a predetermined period; and a RAM data in the second microcomputer is updated with the mentioned transmitted data, thereby enabling an immediate recovery even if the RAM data is destroyed.
On the other hand, the “On-Vehicle Electronic Control Unit” of the Japanese Patent No. 3156493 discloses a technique, in which at the transmission side CPU, a SUM value of the entire transmission data is calculated, and the transmission processing is carried out with a value identical to the foregoing SUM value added to the tail end of a transmission data row; and at the receiving side CPU, a SUM value from the head to the last but one of a received data is calculated, and this SUM value and the rearmost data of the received data are compared. Further, in the case of being the same as a result of comparison, a received data is employed. In the case of being different as a result of comparison, a normal data having been received last time is employed.
In addition, the “Communication Monitoring System” of the Japanese Patent Publication (unexamined) No. 162814/1997 discloses a communication monitoring system, in which a subtracter is provided for doing a countdown at the time of normal communication relative to an error counter that performs a count-up every time any communication error occurs; and the communication error is announced when a count value of the error counter reaches a predetermined value, thereby enabling communication monitoring that is not sensitive to sporadic communication error but immediately announces a continuous communication error.
In the above-mentioned on-vehicle electronic control unit disclosed in the Japanese Patent Publication (unexamined) No. 333901/2002, a normal data is obtained by sum-check of communication data and retransmission processing for error occurrence, at the time of transmitting and receiving control constants. A problem exists in that the presence or absence of data destruction can be detected only by individually reading out and checking control constants once a number of control constants have sequentially been received and stored in the constant setting register.
Moreover, any spontaneous upstream communication packet from the substation side (integrated circuit side) to the master station side (microprocessor side) is not prepared, and reporting from the substation side cannot be carried out without the request from the master station side. Thus, regular requests become necessary in the case where there are regular report data, resulting in a problem that a useless downstream communication takes place.
In the above-mentioned on-vehicle electronic control unit disclosed in the Japanese Patent No. 3346163, a problem exists in the jam-up occurrence of downstream communication due to the fact control constants are transmitted on a regular basis during the operation in the case where there are a number of control constants having to be transmitted to the substation.
Even in the case where control constants are transmitted only at the start of operation and retransmitted during the operation only when a RAM data on the substation side and a ROM data on the master station side is in no coincidence as a result of comparison, a problem exists in that upstream communication is jammed up resulted from the transmission of comparison data to the master station in the case of carrying out the comparison on the master station side; and downstream communication for retransmitting a comparison data is jammed up in the case of carrying out the comparison on the substation side.
In the above-mentioned on-vehicle electronic control unit disclosed in the Japanese Patent No. 3156493, only normal data is obtained by performing the sum-check of a communication data at the time of transmitting and receiving a control constant. A problem exists in that the presence or absence of data destruction can be detected only by individually reading out and checking control constants once a number of control constants have sequentially been received and stored in the constant setting register.
Further, in the above-mentioned communication monitoring system disclosed in the Japanese Patent Publication (unexamined) No. 162814/1997, a problem exists in that a response delay takes place in detecting an error occurrence after the normal communication has continuously been carried out on condition that a threshold for communication error determination is set to be large. On the contrary, a problem exists in that too sensitive error detection is carried out also in the case of trifle and sporadic error occurrence on condition that a threshold for error determination is set to be small.
Moreover, responses to a variety of communication errors of various types, and processing in the case of timeout error or the retransmission processing are not comprehensively described.